Researchers have found that the widespread availability of electric lighting from the 1930s onwards has affected our internal circadian clocks

Not to mention 24 hour TV, internet etc!

Sadly, in this modern world, Man simply cannot go to sleep at sunset & rise at dawn. The way it has evolved, economies would crash & Life As We Know It would end! Anyway....what about the theory that we only sleep in 4-hour intervals with waking periods in between?? (Thread about this on here somewhere.)